Two-signal receiving device



0% 1935- c. F. JENKINS TWO-SIGNAL RECEIVING DEVICE Original Filed July21, 1924 Patented Oct. 22, 1935 iTE sr T E S PATENT oFFicE TWO-SIGNALRECEIVING DEVICE Charles Francis Jenkins, Washington, D. 0., as signor,by mesne assignments, to Radio Corpo ration of America, a corporation ofDelaware 1 Claim.

This invention relates to signal systems, and with particularity to asystem for transmitting and receiving two different messages on a singlewave.

An object of the invention is to provide a method of receiving signalscorresponding to diiferent messages or receiving the signalscorresponding to one message in spaced or modulated groups with theimpulses within the group received at a frequency outside the range ofaudible frequencies, and at the same time utilizing the group spacingfor modulations to receive another message.

Another object of the invention is to provide a method of receivingsimultaneously on a single carrier two separate messages, one of whichis confined to the audible frequency band, the other of which isconfined to the super-audible frequency band.

Another object of the invention is to provide a method of receiving andindicating simultaneously on a single carrier, signals in thesuperaudible range, and other signals in the audible range.

Another object is to provide a method of receiving on a single carrierand indicating signals which may be reproduced visually, andsimultaneously receiving on said carrier signals which may be reproducedaudibly.

In the drawing:

Fig. 1 is a schematic wiring plan embodying the invention; and

Figs. 2 and 3 are illustrative sections of a recording ribbon which hasbeen used therewith.

Referring now more particularly to the accompanying drawing, thereference character I indicates a pair of head phones; 2 a battery incircuit therewith; 3 an electron tube; 4 a filament battery; 5 anantenna coupling; 5 represents a variable condenser for tuning thereceiver to the frequency of the incoming carrier; 5 represents aconventional condenser grid leak combination for enabling the tube 3 toact as a detector although other equivalent detection means may beemployed; 6 a coupling transformer to a circuit having a high frequencylamp 1 therein, for example, a neon or other gas glow lamp; 8 anadjustable condenser therein; 9 a pair of rollers, the rotation of whichgives longitudinal movement to the light snsitive film I0 in thedirection of the arrow; I I indicating rollers to maintain the filmtaut; and I2 is an apertured mask between the light and the film torestrict the exposure of the film to an elemental strip transversely ofthe film.

It is obvious that any audible signals can be heard in the head phones.This is true even when the radio carrier wave has interruptions therein,provided only that the interruptions are frequent enough to be aboveaudibility. These '5 inaudible breaks in the carrier wave, however, canbe recorded on the photographic ribbon, if the lamp 1 is capable oflighting and going out at such high frequencies, and a neon gas filledlamp has this property.

This is true because the condenser 5 shunts the super-audiblemodulations around the telephones I, so that these super-audiblemodulations are confined to the transformer 6. However, in accordancewith well known theory of 15 grid-leak detectors, the tube 3 inconjunction with the grid condenser and leak resistance combination 5detects both the super-audible variations and the audible variations.The audible variations can be heard in the telephones, where- 20 as thesuper-audible variations are passed through the condenser 5, and theprimary of the transformer 6. As is well known, the telephones I areincapable of responding to the high or super-audible frequencies, butcan readily re- .5 spond to the audible frequencies. In other words thecondenser 8 may be tuned to the superaudible frequencies, and thus thecircuit including the transformer secondary and the condenser 8functions to prevent the passage of any low or 30 audible frequencies tothe lamp 1. As is well known, a neon lamp is capable of respondingwithout substantial inertia effects at super-audible frequencies. Theuse of such lamps in sound recording systems is well known, and suchsys- .5 tems are capable of recording frequency variations of the orderof 3000 or more cycles. Consequently all that is necessary is to speedup the movement of the reproducing film l0 so that the super-audiblefrequencies are properly recorded thereon, as indicated schematically inFigs. 2 and 3 of the drawing.

It will be seen, therefore, that (1) the audio signals can be receivedand translated by the head phones; and at the same time (2) theinaudible-frequency breaks in the carrier wave can be recorded on theswiftly running film, each without interfering with the other. It willalso be apreciated that these changes in the carrier 5 wave can just assuccessfully be modulations as long as these frequencies are aboveaudibility.

The reception of carrier wave breaks would be recorded as a' series ofsharply separated dark areas on the film (Fig. 2), whereas a. modulatedll record would appear as different degrees of density along the film,as in Fig. 3.

It will be understood therefore that two different classes of messagecurrents may be received simultaneously on the same carrier wave length.For example one current may correspond to an audible message whileanother current may correspond to a visual message.

Accordingly, while the drawing shows two spe cifio types of signalindicating devices, it will be understood that this is merelyillustrative and that the broad features of the invention may beemployed in any system where two separate messages are to be transmittedon the same carrier.

The principal object therefore is to provide means whereby two differentclasses of signals may be received and detected by means of a singletuning. Various arrangements have been suggested heretofore fortransmitting more than one signal on a carrier, for example theso'-called plural modulation scheme, wherein two separate sustainedwaves are employed, one acting as the carrier proper and the otheracting merely as a modulating wave for the main carrier. In other words,in such plural modulation schemes the carrier proper is not modulateddirectly by one signal device, but is modulated through the intermediaryof another sustained wave. By the present invention this pluralmodulation is avoided since the carrier proper is directly modulated byboth signals without requiring the generation or an intermediatefrequency for one of the signal devices.

Accordingly the present invention provides means whereby a singledemodulator may be employed at the receiving station to detect bothclasses of signals, thus requiring only a single tuning and singledemodulation.

The present application is filed to take the place of an applicationfiled by me July 21, 1924, Serial Number 727,27 2.

This application is related to my Patent No. 1,976,785, issued October16, 1934, which shows apparatus for transmitting a wave of the typeherein described.

What is claimed is:-

In a signaling system the method which consists in transmitting messagesignals to a signal reproducing device only at super-audible irregularsignal frequencies, said signals being transmitted in groups comprisingtwo or more signals, the transmission period of a group being shorterthan the period essential for the establishment 01. an audible wave, andvisually indicating said signals.

CHARLES FRANCIS JENKINS.

